I’m logged into Google with two accounts, my primary account and the shared gmail address. The Tiller addon fails to display when I’m in sheets with my second (shared) account selected. The addon window shows a “drive.google.com refused to connect” error and the browser console shows it failed due to sameorigin restrictions on the iframe:
Refused to display 'https://drive.google.com/accounts?authuser=4&continueUrl=https://docs.google.com/macros/u/4/d/XXXXXXXXXXXXXXX/iframedAppPanel?eei%XXXXXXXXXX-XXXXXXXX-XXXXX-XXXX-XXXXXXXX&ddrp=1#' in a frame because it set 'X-Frame-Options' to 'sameorigin'.
Clicking on the link that gets rendered I get an account picker showing all my signed-in accounts but interestingly my shared account is greyed out with an error stating: “Unavailable unless you sign out of all other Google Accounts and then sign in to this one. Other options”